down the rabbit hole i go...hammerli 850 hpa conversion

[Ammo Maniac]

Hi -- to the experts on this thread. I thought it was more appropriate  in this thread than to start a new one .. hope that is ok  I have recently bit the bullet -- and decided to convert my 850 4.5mm to HPA. So i have done some of the mods (valve mod + dominator spring) - however, onceI put it back together i have a new problem. The gun fires -- but no air. So I have to pull everything apart to confirm what is going on... my most pressing issue now -- is how to degass this safely ?

[Tucobenedicto]

Hi,i suppose there is a paintball bottle and regulator in your setup,a common issue was the check valve on the regulator bonnet not pushed enough by the adaptor.
On my 850 i removed the check valve and the adaptor is totally drilled.
To degass i suggest to loose the fill port or the gauge,just a bit,stop when it start hissing and wait until pressure drops.

[Ammo Maniac]

Thank you for the reply.  2 questions. Can you explain what parts you drilled out and what part you removed on the regulator / adapter?

On the lossening of the gauge - i put some thread tape before installing it.. and loosend it a bit.. no air hissing yet.. so i wasnt sure how much to go before it poses and danger to me trying to loosen it.. dont want it to go missile on me... lol

[Tucobenedicto]

Drill the adaptor is not mandatory,i drilled mine for better flow,but you can simply tap out the rod inside.
The part of the regulator you screw in to the adaptor has a spring loaded brass pin or a tiny ball. When the adaptor is screwed in the valve,the steel piercing pin on the valve pushes the adaptor rod backwards to force the pin or ball open and the valve pressurize.
Can happen the travel of the rod is not enough to open the pin/ball valve on the regulator,this is one of the reasons i removed this system and i keep my bottle always on the rifle.
To remove the check valve on the regulator you must unscrew the top of the regulator and remove the small spring and pin/ball.
I am sorry but y lost all my photos about regulators.
About degassing,if you use a manual pump,take a few pumps until you hear the fill nipple click open,then open carefully the degassing knob on the pump and let the air escape very slowly.

[Tucobenedicto]

Found this:
The parts you must remove are  S18,S19,S20 spring,pin and o ring.

[Ammo Maniac]

Will be trying your suggestions.  Thank you for the help. I got my tank currently bleeding off.  Will try those mods.

[Ammo Maniac]

So,, I have tried all those suggestions.

Let me explain my setup a bit -- and the mods I have done.

Umarex 850 in 4.5mm
22Ci bottle with HPA adapter that can do 800psi -> 2200 psi
adapter fitting to rifle
Valve mod done - 2 holes drilled
Upgraded the spring from standard to dominator

Observations :
1) I did not notice any difference in cocking effort from the original spring to the new dominator spring. ( wonder if they supplied me an incorrect part - both spring looked and felt identical. - not sure if there was a way to tell the difference between the original and a dominator spring.
2) I have tried multiple settings on the hpa regulator - as I had suspected maybe the psi was set to high -- according to the settings -- my belville stack should be at around 1200 psi.
3) I have taken out the entire power train that is the bottle + HPA + adapter + valve. and tested for leaks as well as to confirm that air is coming right up until the valve.  - It is. so I was happy with that.

With all the above - when I load and fire -- all i hear is the click of the hammer -- but no air release.
-- I did try with the original Co2 adapter -- works as normal. fires

So -- do I have a bad spring ? -- do I need to pre-load or is there something else that I am missing to run this on HPA ?

-- appreciate the time and help in helping me get this sorted.

[Tucobenedicto]

Y think you have the wrong spring,the dominator spring look different from the original spring and the cocking effort become high.
If your pressure is a bit more than extimated, you are over the capability of the OEM spring,so the valve can't be open.

[Ammo Maniac]

The spring sent to me - looks and feels identical to the one that is on the rifle (standard) . length wise - as well as tension.

So, I'm not sure how the supplier of the spring is going to deal with the issue (bagnallandkirkwood) (edit - So I have spoken to the supplier -- they advised that the spring is for the UK market  - which is NOT the original spring) - so therein possibly is my issue) - is there any other quick fix around this -- like a generic type spring that I can get and maybe cut down -- etc..

Do you recommend that I shim the current spring setup or pre-load it ?  --  I didnt want the gun to fire to "hot" in 4.5.

[Tucobenedicto]

Now is clear what happened,they send to you a spring rated for the legal UK limit (12FPE).
Shimming the spring is an option,when i started playing with my 850, i shimmed the spring with a plastic tube at the base of the spring guide, this worked at a pressure about 1400psi.
You can shim with a 5-6mm lenght of tube,not much over or the rifle won't cock.
A possible source of a spring is Germany,they selled an "export" version of the spring,but i am thalking of many years ago.
Some industrial hardware store normally sell springs you can cut to lenght,or you can try here:
https://www.industrial-springs.com/products/compression-springs
taking some measurement of the original spring you can determine the compression force using their tables.